1. Field of the Invention
The present invention relates to a method for controlling a masking block overlapped to prevent a particular subject requiring privacy protection from being exposed.
2. Description of the Related Art
Recently, with a digital video recorder (DVR) in common use, a monitoring camera installed at a place requiring security takes a photograph of a subject to be monitored and image data of the photographed subject can be stored in the DVR. However, since an image of the subject photographed by the monitoring camera can also include faces of unspecified individuals, denunciation on privacy infringement is being raised.
For the purpose of protecting privacies of the unspecified individuals, there has been proposed a method for displaying a masking block such as a mosaic image in an overlapped way. This method is a method for overlapping an image including the masking block for hiding only a subject with privacy to be protected with the image of the subject to be monitored (hereinafter referred to as “monitor image”).
FIG. 1 is a diagram illustrating a configuration of a general monitoring camera 100 with its zoom magnification adjustable, including a zoom lens 10, a focus lens 11, an iris 12, a charge couple device (CCD) 13, an analog/digital (A/D) converter 14, a digital signal processor 15, a controller 16, and a memory 18.
In addition, the monitoring camera 100 further includes a masking block generator 17 for generating the masking block such as the mosaic image to be overlapped to hide an image of a particular subject included in a monitor image.
As shown in FIG. 2, when privacy protection for a subject A of subjects A, B, C, D and E, which are included in the monitor image to be photographed in a state where zoom magnification is 1 (zoom state=×1) is required, the controller 16 controls operation of the masking block generator 17 and the digital signal processor 15 such that a masking block of a certain size is overlapped with an image of the subject according to a key input by a user.
More specifically, when the user specifies a start position coordinate value (Xs, Ys) and an end position coordinate value (Xe, Ye) of a masking block to be overlapped using a mouse or a directional key, the controller 16 controls the masking block generator 17 to generate the masking block corresponding to the specified coordinate values and controls the digital signal processor 15 to overlap the generated masking block with the monitor image such that the subject A included in the monitor image is not displayed by the masking block.
In addition, for the purpose of photographing a place to be monitored at various angles, the monitoring camera 100 can be mounted on a pan/tilter 200, which is an apparatus for rotating the monitoring camera 100 vertically and horizontally, as shown in FIG. 3. The vertical rotation and the horizontal rotation are referred to as “tilting” and “panning”, respectively.
When the monitoring camera zooms in from ×1 to ×4 in zoom magnification, or is tilted vertically or panned horizontally, the size and/or position of an image of the subject appearing in the monitor image are varied between after and before changing the zooming and, tilting and/or panning.
However, under a condition where the masking block for hiding the image of the particular subject included in the monitor image is overlapped with the monitor image, when a zoom lens of the monitoring camera is zoomed and/or the monitoring camera is rotated by the pan/tilter 200 such that the size and/or position of the subject appearing in the monitor image is changed, there is conventionally no method for precisely hiding the particular subject with the changed size and/or position by correspondingly changing the size and/or position of the masking block.
In addition, if the CCD 13 is not correctly mounted on a printed circuit board (PCB), for example, when a center axis of the CCD 13 is not coincident with an optical axis of the zoom lens due to an error in a manufacture process, as shown in FIG. 4, when the zoom magnification is increased, the image of the subject A positioned at the center of the monitor image in FIG. 2 is deviated from the center of the monitor image which is zoomed in while being enlarged in size. Accordingly, even when the size of the masking block is adjusted to correspond to the increased zoom magnification, the masking block with the adjusted size cannot exactly hide the subject deviated from the center of the monitoring image and appearing with its enlarged size.
As shown in FIG. 6, if the monitoring camera 100 is not correctly mounted on the center of the pan/tilter 200, a trace along which the image of the subject A included in the monitor image photographed by the monitoring camera 100 actually moves by the panning or tilting becomes an abnormal trace different from a moving trace in a state where the monitoring camera 100 is correctly mounted on the center of the pan/tilter 200. Accordingly, even when the position of the masking block is changed to correspond to a normal panning or tilting, the masking block with the changed position cannot exactly hide the subject moved along the abnormal trace.
In addition, when the monitoring camera is powered off, since information on a set masking block is not stored, a problem arises in that the user has to repeat a setting operation to display the masking block.
On the other hand, a remotely controllable monitoring camera can hide an image of a particular subject requiring protection of privacy as a remote user specifies the masking block using an input device such as a mouse or a directional key prepared in the DVR to control the monitoring camera. However, since there is conventionally no method for specifying the masking block for a remotely uncontrollable monitoring camera, there arises a problem of insufficient protection of privacy.